The present invention relates to a method and an apparatus for making cans such as cans for storing and preserving food, cans for containing paint and the like. More specifically the invention relates to the production of cans, which are made from three pieces, namely a bottom part, a body part and a lid or closure and to cost efficient production of cans in small batch sizes.
A large number of different methods and apparatuses for making cans are known. Cans are typically produced in large numbers by specially crafted tools and machines and thereby the production cost for each piece can be kept at a reasonable level. On the other hand, facilities for producing cans are custom made and adapted to produce one specific can size and can shape and the lacking flexibility results in relatively high costs for changing can type.
It is an object of the present invention to provide a method and an apparatus enabling fast and cost efficient shifts between cans of different sizes and shapes thus enabling smaller batch sizes in can production.
Accordingly the present invention provides a method of making a tubular can body from a blank of sheet material having a pair of opposite co-extending rim portions, method comprising gripping the rim portions by gripping means, mutually moving the gripping means so as to bring the rim portions into adjacent positions, and interconnecting the rim portions of the blank by a seam so as to form the tubular can body, while a major intermediate portion extending between the rim portions remains unsupported, at least internally.
The sheet blank is thus formed into a tubular can body without using any internal mandrel of a predefined shape. This method enables cans of different sizes to be made by use of the same tools without any reconfiguration of such tools. Only the gripping positions of the gripping means have to correspond to the size of the blank of sheet material.
Each of the gripping means may preferably be provided with at least two linear degrees of freedom and one rotational degrees of freedom. Thereby easy supply and discharge of respectively raw material and can bodies will be achieved. The gripping means should preferably be actuated by power driven means, controlled by a control system so as to enable forming of can bodies of different size. In one embodiment of the invention the gripping position can be set automatically by means of detectors determining the size of the blank of sheet material being processed.
The interconnecting seam can be made by interlocking engagement folded, hook-shaped rim portions, by seaming, welding, gluing, soldering or any other conventional seam making process. Preferably seam is made by interlocking pre-folded rim portions of the blank. The provided 3 degrees of freedom enables the the pre-folded rim portions to be interlocked while the folded parts are being pressed together.
According to a further aspect, the present invention provides a method of forming a tubular can body into a desired cross-sectional shape by means of a shape-defining device having a plurality of co-extending elongated contact surface parts for contacting the can body, said method comprising inserting the tubular can body in the shape-defining device such that the contact surface parts thereof each extends substantially axially in relation to the can body and adjacent to the inner or outer side surface thereof, and mutually moving the contact surface parts laterally into contact with the can body side surface or surfaces at peripherally spaced positions so as to peripherally extend the can body and impart the desired cross-sectional shape thereto. The tubular can bodies being formed into a desired cross-sectional shape may be formed by the method described above or by any known method. However, by using this shape-defining device it is less critical whether the cross-sectional shape of the tubular can body being formed has an accurate circular cross-section or any other cross-sectional shape. As mentioned above, this way of forming the can body into a predefined shape can be performed in connection with the above described method of making a tubular, cylindrical can body, or it can be performed in connection with can bodies made in any other way, such as by extrusion, moulding etc. The method enables different shapes to be imparted into the can body just by an exchange of simple tools and therefore a relatively small number of can bodies may be shaped rather cost efficiently.
The lateral movement of the contact surface parts may preferably be actuated by power driven means controlled by a controller in a way enabling a variable stroke length of the lateral movement. As an example the contact surface parts may be moved by pneumatically, hydraulically or electrically driven actuators controlled by a computer system. Cans of different size and/or shape may thus be formed without any physical changes to the shape-defining device.
According to another aspect of the invention, the tubular can body, or a sheet blank may be formed into a desired cross-sectional shape, by passing the blank or the tubular body wall through the nips of at least three pairs of co-operating, rotating shape defining rollers extending in the same general direction, and mutually transversely or rotationally moving said pairs of rollers so as to provide said desired cross-sectional shape. Each pair of rollers may be moved one by one or simultaneously and they may be moved either linearly or rotationally in relation to the path of the sheet or can body. The distance between the rollers in a pair of rollers may be varied so as to enable various sheet thickness or wall thickness of the can bodies. This way of forming a tubular can body into a desired cross-sectional shape may preferably be combined with the earlier described way of making a tubular can body from a blank of sheet material, thus providing a unified flexible means for forming cans from blanks of a sheet material.
Another aspect of the invention relates to a method of flanging, beading and curling a tubular body, such as a can body, or a sheet blank therefor. The sheet blank or the tubular body wall is passed into the nip of a pair of co-operating, rotating rollers having at a first end thereof flange forming means, which form a flange at an adjacent first end of the tubular body or blank and bead forming means being axially spaced from the flange forming means and forming a bead in an intermediate part of the blank or tubular body, and engaging a curling tool with an opposite, second end portion of the blank or body so as to curl said second end portion. In a preferred embodiment of the invention the flanging, beading and curling may be performed simultaneously with the forming of the sheet or can body according to the previous described way of forming a can body by use of rollers. The same pairs of rollers or at least the one pair of shape defining rollers may be used. The rollers must for this purpose be adapted for the flanging by means of a flanging edge at one end of at least one of the rollers. This could be an end portion of one of the co-operating rollers having an increased diameter and extending axially beyond the adjacent end of the other roller of said pair. The rollers must furthermore be adapted for beading by bead forming means such as an peripherally extending ridge formed on one of the co-operating rollers and a ridge receiving peripheral groove formed in the other of the co-operating rollers. A curling tool can preferably be movably positioned so as to enable engagement with an opposite end of the blank or body in relation to the end where the flange is made.
The seam of the tubular can body may be made in any conventional manner. As an example, the rim portions of the can body blank may be pre-formed so as to define seam parts, which are interlocked and subsequently flattened so as to form said seam. This procedure enables a simple and cheap tool for making the seam. Alternatively, the seaming tool may bend both rim portions, provide the interlocking engagement, and subsequently flatten the bent rim portions so as to stabilise the interlocking engagement. Standard tools for these procedures are generally available on the market.
A tubular can body may be seamless, for example when it has been made by extrusion. Usually, however, the can body has a longitudinally extending seam. When such can body is to be formed into a desired cross-sectional shape by the method described above the longitudinally extending seam is preferably gripped between one of said contact surface parts and an oppositely arranged backing member. Thereby it may be avoided that the peripheral stresses, which are generated in the can body wall by the shape-defining device, are transferred to the seam so as to cause defects or leakage thereof.
The desired cross-sectional shape of the tubular can body may be obtained by arranging all of the contact surface parts within the can body and by moving at least one of them radially outwardly, or by arranging at least two and preferably at least three contact surface parts within the tubular can body and one or more radially outside the can body and by moving at least one inner contact surface part radially outwardly and/or at least one outer contact surface part radially inwardly so as to bring all of the contact surface parts into contact with the can body and define the desired cross-sectional shape and so as to provide the necessary peripheral stress in the can body wall to obtain the desired permanent shape. This means that all of the contact surface parts may be moved transversely or radially in relation to the can body, or one or more of the contact surface parts may be maintained substantially stationary in relation to the can body during said mutual lateral movement of the contact surface parts.
As mentioned above, all of said elongated contact surface parts can be located within the inner space of the tubular can body, and at least one of the contact surface parts may then be moved transversely in relation to the other contact surface parts, so as to bring all of said contact surface parts into abutting engagement with the inner side surface of the can body. Alternatively, however, a first number of said elongated contact surface parts may be located in the inner space of the tubular can body and a second number of said elongated contact surface parts may be located outside the tubular can body, at least one of said first number of contact surface parts being moved laterally outwardly into contact with the inner side surface of the can body, and/or at least one of said second number of contact surface parts is moved laterally inwardly into contact with the outer side surface of the can body, so as to bring all of said contact surface parts into abutting engagement with the inner or outer side surface of the can body. In this way the shape of the can body can be imparted both from the outside of the can body and from the inside of the can body or from both sides in combination. This means that seen from the outside the shaped can body may have convex parts only or a combination of convex and concave surface parts.
The elongated contact surface parts may comprise a plurality of rod members having a circular or polygonal cross-sectional shape. Each such rod members may contact the can body along a longitudinal extending, narrow contact area only so as to form a plain inner or outer sharp or rounded corner part on the can body. It may be desired to form corner parts or other wall parts of the can body having a more sophisticated cross-sectional shape. Thus, each of the contact surface parts may have a cross-sectional shape, which is substantially complementary to the desired cross-sectional shape of can body wall parts at respective, peripherally spaced positions of the can body. As an example, apart from sharp edged, rounded or otherwise shaped corner portions the contact surface parts may be used for forming decorative embossments in the side walls of the can body.
As indicated above, the contact surface parts are preferably defined on a plurality of elongated, substantially co-extending rod-like members. In a preferred embodiment the rod-like members are sleeve-like members of which at least some are removable mounted on a core, such as a rod or shaft. This allows for fast and easy exchange of contact surface parts, e.g. for changing the desired cross-sectional shape or for replacement of worn or otherwise defect surface parts. The sleeve-like members can be made from any suitable material, such as from metal or another hard or hardened material, or they can be made from a resilient material, such as a resilient rubber or rubber-like material depending upon the materials characteristics of the sheet material from which the can body has been made.
The can bodies may be made from any suitable material, including plastics material. However the can bodies are preferably made from a conventional sheet metal, such as tinplate, aluminium or aluminium alloys.
According to a further aspect, the present invention relates to a method for fastening a bottom part to a can body, said method comprising positioning the bottom part at one end of the can body such that a rim portion of the bottom part is in abutting engagement with a radial flange formed at said one end, rotating the can body in relation to at least one seaming such as curling, bending or folding tool, and moving said seaming tool radially in relation to the can body along a predetermined path corresponding to the cross sectional shape of the can body. The seaming tool may be moved radially in relation to the can body by any suitable moving means. As an example, the seaming tool may be movable by means of an actuator, which is controlled by a computer. The computer may control the actuator in accordance with a program loaded into its memory. Thus the actuator may be controlled to move the tool radially in relation to the can body so as to follow the pre-determined path corresponding to the cross sectional shape of the can body. In this way cans of different size and with quite different cross-sectional shapes may be produced by means of the same device, provided that the relevant program or pre-determined path be loaded into the memory of the computer. The pre-determined path may be loaded from a computer aided design tool or from a similar CAD/CAM related tool.
Alternatively, the means for radially moving the seaming tool may comprise means for biasing the seaming tool into engagement with said rim portion and/or with said radial flange at a predetermined substantially uniform biasing force during said relative rotation of the can body and the tool, so as to bend or fold said rim portion and/or said flange. This is preferably done by means of force-controlled actuators. Contrary to traditional ways of interconnecting bottom parts with can body parts, where a predetermined path is followed, the advantage of using force controlled actuators is that such actuators follow the specific shape of a given can body and bottom assembly line and thus compensate for tolerances.
In a preferred embodiment of the invention the can bottom is being fastened to the can body by means of a plurality of peripherally spaced seaming tools, moved or biased into engagement with said rim portion and/or with said radial flange. Each of the tools being adapted to perform different bending or folding operations so as to form a seam.
As a further possibility, each of one or more of the tools for seaming such as curling, bending or folding operations may be moved along a radial guide member and biased into engagement by spring means or by means of a linear electric motor. These solutions offer a cheap and reliable fastening operation and flexibility and high performance in the fastening operation, respectively.
In a preferred embodiment of the invention the method for fastening the can bottom part to the can body part includes a controlled interdependency between the radial movement of the tool in relation to the rotation of the can body and the shape of the can body. This enable fastening of a can bottom part to a can body part having non-circular cross-sectional shape such as a square or triangular shape. When the tool passes a corner or sharp edge the rotational speed of the can body is decreased in order to allow the tool to change its direction.
According to another aspect the present invention relates to an apparatus for can making according to the previously mentioned method.